[httpclient] Update usage help for `-3` option
[httpclient] Update usage help for `-3` option

cwyang/h2o,devnexen/h2o,yannick/h2o,yannick/h2o,yannick/h2o,devnexen/h2o,devnexen/h2o,devnexen/h2o,devnexen/h2o,yannick/h2o,cwyang/h2o,h2o/h2o,yannick/h2o,cwyang/h2o,h2o/h2o,cwyang/h2o,h2o/h2o,devnexen/h2o,cwyang/h2o,cwyang/h2o,yannick/h2o,yannick/h2o,h2o/h2o,h2o/h2o,h2o/h2o,yannick/h2o,devnexen/h2o,devnexen/h2o,cwyang/h2o,devnexen/h2o,yannick/h2o,cwyang/h2o,h2o/h2o,h2o/h2o,h2o/h2o